Aphids

What are Aphids?

Aphids have a well-earned reputation, as one of the most infuriating and destructive garden pests in NZ. Scroll down to read all about them, or press the green button to go straight to the fix!

Aphids cause damage to plants directly by feeding on plant sap, or or by passing on harmful viruses (which they inject into your plants in their saliva). Aphid feeding severely weakens plants, so host plants also become less resistant to fungal and diseases.

There are 100+ different species of aphids in NZ. They all have different preferences in the plants they attack, but between them they feed on fruit trees, citrus, roses, camellias and a wide range of vegetables.

Black Citrus Aphids (Aphis citricidus) with pale shed skins visible.

Identifying Different Types of Aphids

Here are some of the most commonly encountered pest aphids, with their preferred host plants:

• Black Citrus Aphids (Aphis citricidus) are glossy black or dark brown. You'll see them clustered in huge numbers on the growing tips of citrus trees in spring. These aphids are usually the culprits when leaf curl appears in citrus trees.
• Onion Aphids, AKA Black Aphids (Neotoxoptera formosana) are a serious pest of garlic, shallots, onions, chives, leeks and other alliums, causing yellowing, wilting and dehydration of leaves, and poor harvests.
• The Cabbage Grey Aphid (Brevicoryne brassicae) is greyish-green, with a powdery-looking waxy coating. It feeds on all types of brassica crops, usually hiding on the underside of leaves.
• The Green Peach Aphid (Myzus persicae) has a special liking for stonefruit, but it happily feeds on a wide range of vegetable crops (including brassicas) through summer and autumn.

Onion Aphids (Neotoxoptera formosana)

Aphid Species, continued:

• Woolly Apple Aphids (Eriosoma lanigerum) have a preference for apple and pear trees; they can distort new growth and damage buds, which inhibits the harvest. They are very distinctive because they cover themselves in a white fluffy woolly substance, which looks like clumps of cotton wool stuck to branches. The easiest way to control them is with a single winter spray of Yates Lime Sulfur, while the tree is leafless.
• The Rose Aphid (Macrosiphum rosae) is common pest of roses. Green or pinkish coloured aphids can be seen swarming on flower buds and tender growing tips.
• Strawberry Aphids (Chaetosiphon fragaefolii) are pale yellow in colour. These aphids spread strawberry mottle virus: a very damaging disease that stunts growth, yellows leaves and impedes fruiting. During spring they're often found on the underside of strawberry leaves, so good spray coverage is important to control them effectively.
• The Melon Aphid (Aphis gossypii) prefers to feed on curcubits, like watermelons, cucumbers, pumpkin, luffa and zucchini.

Cabbage Grey Aphids (Brevicoryne brassicae)

Why are Aphids so Persistent? 

Many aphid species are capable of reproducing without any males around (this is called parthenogenesis). This explains why aphid colonies can increase in size so rapidly: during warm weather females mostly birth live young, without needing to mate. In warmer climates, they can do this all year round. In cooler climates, aphids overwinter by mating and laying eggs, that hatch out in spring.

Aphids typically pass through 4 nymph stages (instars) before the adult stage. As they moult, they leave behind their old skin casts (these will often be visible as white objects on leaves or buds). Aphid life cycles can be completed in 10-14 days in warm weather, and there can be more than 20 generations per year, depending on the climate and the species.

Adult aphids without wings are the norm when the colony isn’t overcrowded. When a colony needs to migrate from an over-wintering site, or from dried-out plants, or when conditions become too crowded, winged adult aphids develop, to allow them to move to new host plants.

Rose Aphids (Macrosiphum rosae), showing dried cast-off skins

Symptoms of Aphid Infestation

New growth is often covered in dense clusters of feeding aphids: they prefer to feed on fresh young shoots, where plant sugars are concentrated. Aphids can also be found on flower buds, or underneath older leaves. New leaves can be twisted and distorted. Buds may fail to open. You may notice that fruit fails to set, or experience early fruit drop.

Leaves are often covered in unsightly cast-off skins from the nymphs. These small, papery-looking translucent or white 'moults' are usually accompanied by shiny, sticky honeydew.

Honeydew is a combination of unused sugars and water, excreted by the aphids. Honeydew provides an ideal environment for sooty mould fungus to grow, so this black, sooty-looking substance covering leaves is a common symptom of an aphid infestation.

Likewise, honeydew is a valuable food source for ants, so lines of ants are another common symptom of an aphid infestation. Removing the aphids that create the honeydew will solve the sooty mould (and ant) problem.

Honeydew is also very attractive to ants, so they're often visible around aphid infestations. Fascinatingly, ants are known to protect aphids from predators, a little bit like farmers care for cows...so the ants can harvest the honeydew!

Ants 'farming' aphids for their sugary honeydew

How to Get Rid of Aphids

Our go-to product for aphids is Yates Nature's Way Vegie, Citrus & Ornamental Spray, a clever pyrethrum and oil combination insecticide, with twin modes of action against insect pests. It's BioGro-approved as an organic input, with a 1-day withholding period between spraying and harvest.

For tomatoes, stonefruit and ornamentals, Yates Mavrik Insect & Mite Spray concentrate, or the handy ready-to-use Yates Mavrik Insect & Mite Gun are popular choices, because they're fast and effective.

For roses and ornamentals, Yates Super Shield Rose Spray is a great all-rounder that also controls diseases.

If you take care not to kill natural predators, like ladybirds, or parasitic wasps, they'll help you control aphids. Ladybird larvae (which look like tiny bird droppings) are voracious eaters of aphids. Parasitic wasps lay their eggs inside aphids, turning the unfortunate hosts into light brown, mummified empty shells, with exit holes in them. Both of these predators will reduce aphid numbers rapidly when they arrive. If you don't want to leave residue that might harm these beneficial insect predators, Yates Nature's Way Vegie Insect Spray Natrasoap is a great solution.

Woolly Apple Aphids (Eriosoma lanigerum)

Plants Impacted

• Citrus
• Fruit Trees
• Berries
• Vegetables
• Roses
• Ornamentals